Cover for secondary battery

ABSTRACT

By using a rivet which serves also as a terminal member, and a sealing member which serves also as an insulating member, the terminal member and the insulating member can be omitted, thereby forming the lid of the secondary battery from only three parts, i.e. the body, rivet and sealing member. The sealing member includes a cylindrical portion and a flange portion which are separate members. The cylindrical portion is formed by cutting a fluororesin tube. The flange portion is formed by punching a polypropylene resin sheet. Thus, the number of parts can be reduced to four, so that it is possible to reduce the parts cost and manufacturing cost as compared to conventional lids.

BACKGROUND OF THE INVENTION

The present invention relates to a secondary battery, and moreparticularly to an improved type thereof which can be manufacturedinexpensively.

The increased prevalence of cellular phones is an eye-opener. As powersources of such cellular phones, lithium ion batteries are typicallyused in place of nickel-cadmium batteries and nickel-hydrogen batteries.

Since lithium ion batteries are higher in working voltage and larger inenergy capacity as compared to nickel-cadmium batteries, they aredurable and have such electrical properties that they are less likely todeteriorate due to additive charging. Further, lithium ion batteries arelightweight. Due to these properties, lithium ion batteries areadvantageous for use in light, thin, short and small devices such ascellular phones and video cameras.

But, while lithium ion batteries have the above-described advantages, aproblem is that they are expensive.

An object of the present invention is to provide a lithium ion batterywhich is less expensive than the conventional lithium ion battery.

SUMMARY OF THE INVENTION

In order to solve the above object, the structure of a lid of a lithiumion battery has been improved in the present invention so that it can bemanufactured at a low cost to thereby reduce the cost of the entirelithium ion battery. First, referring to FIGS. 2 and 3, the structure ofthe lid of a conventional square-shaped lithium ion battery will bedescribed.

The lid 10 of the square-shaped lithium ion battery shown in FIG. 2 hasa body 1 formed of an iron plate plated with aluminum or nickel, and hasa rectangular shape corresponding to the shape of a housing on which itis placed. To the center of the body 1, a rectangular terminal member 2for mounting a lead wire is joined by a rivet 5 through a sealing member4 together with an insulating member 3 slightly bigger than the terminalmember 2. In the figures, thin-wall portions 6 of the body 1 function asa safety valve if the internal pressure of the housing rises. A hole 7is provided to pour an electrolyte.

Next, a combined form of these parts of the lid 10 is described withreference to FIG. 3, which is an exploded perspective view.

As shown in FIG. 3, a hole 1 a for mounting the terminal member 2 andthe insulating member 3 is formed at the center of the body.Through-holes 2 a and 3 a are also formed in the center of the terminalmember 2 and the insulating member 3, respectively, to mount theterminal member 2 and the insulating member 3 to the body 1.

The sealing member 4 mounts the terminal member 2 and the insulatingmember 3 to the body 1 and is a cylinder having an outward flange at oneend thereof. A cylindrical portion 4 b has such an outer diameter as tobe fitted in the mounting hole 1 a at the center of the body 1. Thesealing member 4 is formed by injection-molding a polypropylene resin.Such members are mounted to the body 1 in the manner described below.

First, as shown in FIG. 3, the terminal member 2 and the insulatingmember 3 are superposed with the insulating member 3 under the terminalmember 2 so that the centers of their respective through-holes 2 a and 3a will align. Then, the terminal member 2 and the insulating member 3are placed on the body 1 with the centers of the respectivethrough-holes 2 a, 3 a of these members 2, 3 aligned with the center ofthe mounting hole 1 a at the center of the body 1.

Next, the cylindrical portion 4 b of the sealing member 4 is insertedinto the through-holes 1 a, 2 a and 3 a of the three members from theback of the body 1. The rivet 5 is then inserted into the cylindricalportion 4 b of the sealing member 4 from the back of the body 1 andjoined by caulking. Now the cover 10 is in the state shown in FIG. 2.

A lead wire (not shown) is mounted by welding the lead wire to thesurface of the terminal member 2, which has thus been mounted to thebody 1. In order to ensure welding, the terminal member 2 requires anarea having a large occupying rate relative to the body 1 as shown inthe figure.

Due to advancements of welding technology, however, it became possibleto reduce the required area to be welded to a value substantially equalto the area of the end face of the rivet 5 after caulking.

Thus, by using the rivet 5 as the terminal and welding lead wire to therivet, the terminal member 2 can be omitted. This makes it possible tomanufacture the lid 10 at a low cost due to a reduction in the number ofparts.

Thus, in the present invention, the rivet 5 is also used as the terminalmember 2 to reduce the number of parts to four.

Further, by making the sealing member 4 an insulating material and usingit also as the insulating member 3, it is possible to further reduce thenumber of parts to three (see FIGS. 1B and 1C).

Moreover, according to the present invention, the sealing member 4 mayconsist of a cylindrical portion 4 b and flange portion 4 a (FIGS. 1Aand 1B). Advantages of this arrangement will be described below.

Heretofore, the insulating member 3 was, as described above, formed byinjection molding of inexpensive polypropylene resin. But if the housingis made thin to reduce the size (thickness) of the battery, theinfluence of heat produced in welding the housing and the lid 10together increases, so that the propropylene resin, which is inferior inheat resistance, cannot withstand the heat. Thus, it was impossible toreduce the size. Instead of polypropylene resin, using a fluororesin,which is superior in heat resistance, is considered.

But a fluororesin is not only expensive but is also difficult toinjection mold, so that in order to perform injection molding, a specialgrade one has to be used. Thus, the cost is high as compared with othermaterials.

In the present invention, the sealing member 4 comprises the cylindricalportion 4 b and the flange portion 4 a, as shown in FIGS. 1A and 1B,which are separate from each other and simple in shape.

With this arrangement, disks for such simply shaped cylindrical portion4 b and flange portion 4 a can be manufactured by punching or extrudinga sheet material. Such work is inexpensive in cost. Thus, a fluororesinmay be used, which is expensive but superior in heat resistance, it ispossible to obtain a product more inexpensive than conventional in theend.

Also, in the entire sealing member 4, the flange portion 4 a is aportion for which high sealability is not as required as it is for thecylindrical portion 4 b but insulating properties are mainly requiredfor the flange portion 4 a. Thus, even if the flange portion 4 a isdeformed under the influence of heat buildup during welding, this willpose no significant problem. Thus, the flange portion 4 a may be formed,not from an expensive fluororesin, but from a sheet member ofinexpensive polypropylene resin by inexpensive punching. This furtherreduces the manufacturing cost of the lithium ion battery.

The above description has been made with reference to a lithium ionbattery. But this invention is not limited to lithium ion batteries butis applicable to other secondary batteries such as nickel-cadmiumbatteries and nickel-hydrogen batteries if the lid has the samestructure for the connection of the lead wires.

Other features and objects of the present invention will become apparentfrom the following description made with reference to the accompanyingdrawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B and 1C are sectional views of lids of first, second andthird embodiments of the present invention;

FIG. 2A is a plan view of a conventional lid;

FIG. 2B is a sectional view of the conventional lid; and

FIG. 3 is an exploded perspective view of the conventional lid.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinbelow, referring to the drawings, the embodiments of the presentinvention will be described. For parts identical to those of theconventional lid, identical numerals are used and the descriptionthereof is omitted. In the figures, lead wires connected to the lid arenot shown.

First Embodiment

The embodiment shown in FIG. 1A is a lid 10 having a conventionalterminal member 2 and an insulating member 3. The sealing member 4,however, has a cylindrical portion 4 b and a flange portion 4 a formedseparately from each other.

For the cylindrical portion 4 b for which sealability is especiallyrequired, a fluororesin is used which is, though expensive, superior inheat resistance and is less likely to be deformed even when exposed toheat buildup during welding. It may be formed by cutting a tube madetherefrom.

On the other hand, the flange portion 4 a for which insulatingproperties are mainly required, but for which slight deformation ispermitted, is formed from an inexpensive polypropylene by punching asheet member formed therefrom into a doughnut-shaped disk.

Because for both the cylindrical portion 4 b and flange portion 4 a,ready-made resin tubes and plates are used without using a complicatelyshaped molds, it is possible to manufacture them at a lower cost than asealing member 4 having the cylindrical portion 4 b and flange portion 4a integral with each other.

Second Embodiment

In the embodiment shown in FIG. 1B, by using the rivet 5 which servesalso as the terminal member 2, and the sealing member 4 which servesalso as the insulating member 3, the terminal member 2 and insulatingmember 3 are omitted to form the lid 10 from only three parts, i.e. thebody 1, solid rivet 5 and sealing member 4.

For the sealing member 4, as with the first embodiment, the cylindricalportion 4 b and flange portion 4 a are formed as separate elements. Thecylindrical portion 4 b is formed by cutting a fluororesin tube, and theflange portion 4 a is formed by punching a polypropylene sheet member.

Since this embodiment has no terminal member 2 or insulating member 3,the parts cost and manufacturing cost are less expensive.

Third Embodiment

In the embodiment shown in FIG. 1C, instead of splitting the sealingmember 4 into the cylindrical portion 4 b and flange portion 4 a as inthe second embodiment, an integral sealing member 4 is used, which isformed by injection molding.

As described above with regard to the second embodiment and which can beseen in FIG. 1C, the rivet 5 serves as the terminal member 2, and thesealing member 4, being integrally formed, serves as the insulatingmember 3. Accordingly, similar to the second embodiment, the thirdembodiment of the present invention omits both the terminal member 2 andthe insulating member 3.

Further, by the arrangement according to the third embodiment, thenumber of parts is smaller than in the second embodiment, and can bereduced to only three, i.e. the lid body 1, rivet 5 and sealing member4. Assembly is thus simplified.

But since a complicated shape having the cylindrical portion 4 b andflange portion 4 a integral with each other cannot be manufactured byextrusion molding, it is formed by injection molding. As describedabove, in this method, instead of using a fluororesin, which increasesthe cost, a polypropylene is used.

Thus, since a polypropylene resin is inferior in heat resistance to afluororesin, in order for heat to be dispersed to the surroundings, thisembodiment is applicable to one in which the lid body 1 has largerdimensions, such as its width and length, as compared with thedimensions of the second embodiment.

The structure of the lid 10 of each embodiment is, as described above,applicable to a nickel-cadmium battery, nickel-hydrogen battery or anyother secondary battery. In view of the structure thereof, lids of thesetype of batteries can also be manufactured less expensively than thecost for manufacturing conventional lids.

In this invention, since the lid of a secondary battery is structured asdescribed above, the secondary battery can be manufactured at a lowercost than the conventional secondary battery.

What is claimed is:
 1. A lid of a secondary battery, said lidcomprising: a plate-shaped body having a hole formed therein; a terminalmember; an insulating member, said terminal member and said insulatingmember being superposed on a peripheral edge of the hole formed in saidbody with said insulating member being arranged under said terminalmember; a sealing member having a flange portion at one end thereof andinserted in the hole formed in said body, said sealing member consistingessentially of a flat plate portion having a hole to form said flangeportion, and said sealing member consisting essentially of a cylindricalportion that is separate from said flange portion; and a rivet insertedin said sealing member and caulked in order to join said terminal memberand said insulating member to said body.
 2. The lid of a secondarybattery in accordance with claim 1, wherein said cylindrical portion ismade of a fluororesin.
 3. A lid of a secondary battery, said lidcomprising: a plate-shaped body having a hole formed therein; a terminalmember; an insulating member, said terminal member and said insulatingmember being superposed on a peripheral edge of the hole formed in saidbody with said insulating member being arranged under said terminalmember; a sealing member having a flange portion at one end thereof andinserted in the hole formed in said body, said sealing member comprisinga substantially flat plate portion having a hole to form said flangeportion, and a substantially cylindrical portion that is separate fromsaid substantially flat plate portion of said sealing member; and arivet inserted in said sealing member and caulked in order to join saidterminal member and said insulating member to said body.
 4. The lid of asecondary battery in accordance with claim 3, wherein said cylindricalportion is made of a fluororesin.